Turning the water off and taking out the pressure will reduce the risk of a burst Juliem. Even better if you can drain off the water above ground. When the water freezes it expands and bursts occur between two freezing points because of the pressure built up there. Often outside taps freeze evenly backwards into the wall or ground and therefore don't burst. Insulation, if badly fitted, can make the risk of a burst higher as it can create two freezing points.
Plastic pipe will freeze a bit slower than copper, but it isn't as strong so a burst is just as likely. I went to an unheated property with a mixture of copper and plastic pipes and all the bursts were in the plastic sections.